Re: 80cc powerking motor 30km/h top speed
when you take the head off, assuming there's no damage to the gasket, mark which way it's sitting on there, and put it back the same way. it should be fine. my kit came with two gaskets, and i've taken my head off 15 times, and i'm still using the same one. just be careful not to tweek it when you take it off.
what donnN said about a new plug, if you've got a ngk already, just clean it up. those plugs last a long, long time.
seriously, i think you can solve your problem without spending any money (except for buying some carb cleaner,) on new parts.
everyone always assumes they need a new carb, a new plug, a new motor... but mostly, it's just basic maintenance.
you're gonna get a lot of different advice on this. my advice, is do what's simple and free first. if you do everything i suggested and it still won't run right, then we'll figure out what to do next...
these motors ain't to hard to figure out. they're using the same basic technology that's been around for a hundred years. don't over-think it.
(that's my 2 cents, er... $149 + shipping's worth...)